Observing the magnetosphere through global auroral imaging: 2. Observing techniques

摘要

abstract_textpIn a companion paper four auroral regions were identified. The source of the first three regions is the plasma sheet, whereas the source of the fourth, the region of Alfvenic auroras, is the ionosphere. It is a primary goal of global auroral imaging to identify these source regions. Space-based imaging can be used to obtain ion and electron, mean energy, and energy flux as a basis for such identification. Measurement of direct emission from precipitating ions or their charge exchange products can be used to determine the ion precipitation characteristics. For electrons, it is necessary to use the atmosphere as a spectrometer. Total precipitated energy can be derived from the luminosity of spectral features where the production cross sections are known. The mean energy of precipitation is inferred from the luminosity height profile deduced from (1) collisional quenching of long lifetime emitters, (2) atmospheric composition, (3) degree of O-2 absorption in the UV, or (4) the local atmospheric neutral temperature. There are fundamental advantages in viewing the aurora from space; for example, auroras can be observed in the far ultraviolet range where daylight contamination is much less severe. The various approaches to spaceborne auroral imaging depend on the wavelength selection requirements. UV interferometers show promise of improved light collection efficiency and higher spectral resolution./p/abstract_text